Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

1. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Low boiling point

Large latent heat

High risibility with oil

2. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

3. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Brine

Ammonia

Freon

4. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

Takes place at constant entropy

5. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

6. Which of the following cycles uses air as the refrigerant?

Ericson

Stirling

Bell Coleman

Carnot

7. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

8. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Any one of the above

Always less than unity

Always more than unity

9. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 1

9: 1

1: 9

10. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

None of the above

Page 2 of 4

11. The freezing point of sulphur dioxide is

-75.2°C

-56.6°C

-77.7°C

-135.8°C

12. A bootstrap air cooling system has

Three heat exchangers

One heat exchanger

Four heat exchangers

Two heat exchangers

13. Freon group of refrigerants are

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

Toxic

14. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

15. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Wet bulb temperature

Relative humidity

Dew point temperature

16. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

17. Most thermostatic expansion valves are set for a superheat of

20°C

10°C

15°C

5°C

18. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

1.33

4.33

19. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Centrifugal

Axial

Miniature sealed unit

20. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

Page 3 of 4

21. Rating of a domestic refrigerator is of the order of

5 tons

40 tons

10 tons

0.1 ton

22. For obtaining high COP, the pressure range of compressor should be

Any value

Low

Optimum

High

23. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.376

0.67

0.4

24. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

25. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Detect liquid in vapour

26. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

Absorber

27. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

None of these

Normal cooling

Sub-cooling or under-cooling

28. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

30 bar

2 bar

15 bar

29. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Carnot

Reversed Rankine

Rankine

30. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

Ambient air temperature

Page 4 of 4

31. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Compressor and condenser

Receiver and evaporator

Condenser and receiver

32. The capillary tube, as an expansion device, is used in

Room air conditioners

Water coolers

Domestic refrigerators

All of these

33. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

At critical Temperature

34. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Wet vapour

Dry saturated vapour

Superheated vapour

35. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

36. The boiling point of ammonia is

-10.5°C

-30°C

-33.3°C

-77.7°C

37. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Zero

Positive

Negative

38. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

39. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

40. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Capillary tubes

Condenser tubes

Refrigerant cooling tubes

Share this Now with Friends:

VideRime

A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection